The present invention relates to an .alpha.-SIALON powder and a process for producing it. .alpha.-SIALON is a solid solution of an .alpha.-type silicon nitride represented by the general formula M.sub.x (Si,Al).sub.12 (O,N).sub.16 wherein M is at least one element selected from the group consisting of Li, Mg, Ca, Mn, Y and lanthanide metals and O&lt;x.ltoreq.2. A sintered product of .alpha.-SIALON is durable at high temperatures and has high strength and hardness as well as excellent corrosion and abrasion resistance, and thus it is expected as a prospective ceramic useful for applications to mechanical parts required to have heat resistance and abrasion resistance, such as cutting tools, drawing dies or mechanical seals. 2. Description of the Prior Art
An .alpha.-SIALON sintered product has been produced by molding a powder mixture comprising Si.sub.3 N.sub.4, AlN and an oxide of M metal (wherein M is as defined above), followed by heating at a temperature of from 1700.degree. to 1800.degree. C.
However, according to this method, three different types of powders are used as starting materials, and the mixing and molding tend to be non-uniform. Consequently, the sintered product is likely to be non-uniform. Thus, it has been difficult to improve the strength or hardness. Besides, the method has a difficulty that is is thereby hardly possible to obtain a powder, since a chemical reaction of the starting materials takes place at the same time as the sintering.